Enhancing sensitivity and robustness of mechanical rotation and position detection with capacitive sensors

ABSTRACT

Described example user interface control apparatus includes a first structure, with a first side, conductive capacitor plate structures spaced along a first direction on the first side, a movable second structure with an auxiliary conductive structure, and an interface circuit to provide excitation signals to, and receive sense signals from, the conductive capacitor plate structures to perform a mutual capacitance test and a self-capacitance test of individual ones of the conductive capacitor plate structures to determine a position of the second structure or a user&#39;s finger relative to the first structure along the first direction.

REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 15/886,173,filed Feb. 1, 2018, and claims priority to, and the benefit of, U.S.Provisional Patent Application No. 62/453,575, entitled “Method ofEnhancing Sensitivity and Robustness of Mechanical Rotation and PositionDetection with Capacitive Sensors,” filed on Feb. 2, 2017, which areincorporated herein by reference in their entireties.

BACKGROUND

User Interfaces (UIs) and human machine interfaces (HMIs) allow a useror operator to control a machine. Capacitive touch interfaces arebecoming more popular, including capacitive touch displays that provideuser input capabilities as well as display of data, graphics or otherinformation to an operator. Capacitive position detection for HMItechnology offers long life time, low implementation costs, and ease ofuse as a sealed fluid and gas proof control element, which is beneficialin areas of operation with explosives and chemical processes. Capacitivesensing can be used for detecting the position of a control actuator aswell as for detecting user touch events. For example, capacitiveposition sensing for rotary and/or linear control elements of an HMI canbe combined with user touch detection. Capacitive sensing systems maysuffer from weak response of conductive structures or of a user's fingerintroduced into the sensitive area of an HMI control device.

SUMMARY

Described example user interface control apparatus includes a firststructure, with a first side, conductive capacitor plate structuresspaced along a first direction on the first side, a movable secondstructure with an auxiliary conductive structure, and an interfacecircuit to provide excitation signals to, and receive sense signalsfrom, the conductive capacitor plate structures to perform a mutualcapacitance test and a self-capacitance test of individual ones of theconductive capacitor plate structures to determine a position of thesecond structure or a user's finger relative to the first structurealong the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a rotational mechanical control apparatusincluding a stationary first structure and a rotatable second structurefor a user interface with capacitive and optical rotational position anduser touch detection.

FIG. 2 is a top plan view of the stationary first structure of thecontrol apparatus of FIG. 1 with schematically illustrated opticalrotational position detection circuitry.

FIG. 3 is a top plan view of the stationary first structure of thecontrol apparatus of FIG. 1 with schematically illustrated capacitiverotational position and user touch detection and interface circuitry.

FIGS. 4-8 are a partial sectional side elevation view taken along line4-4 of the control apparatus of FIG. 1 showing example electric fieldlines during mutual capacitance and self-capacitance measurement forposition and/or user touch detection.

FIG. 9 is a schematic diagram of a mutual capacitance measurementcircuit configuration example in the apparatus of FIG. 4 with noproximate auxiliary conductive structure present.

FIG. 10 is a schematic diagram of a mutual capacitance measurementcircuit configuration example in the apparatus of FIG. 5 in the presenceof an auxiliary conductive structure.

FIG. 11 is a partial top plan view of conductive capacitor platestructures and two example movable auxiliary conductive structures withangular circumferential lengths approximately covering radially outerportions of two neighboring capacitor plate structures.

FIG. 12 is a partial top plan view of conductive capacitor platestructures and two example movable auxiliary conductive structures withangular circumferential lengths approximately covering radially outerportions of three neighboring capacitor plate structures.

FIG. 13 is a partial top plan view of conductive capacitor platestructures and two example movable auxiliary conductive structuresapproximately covering the circumferential and radial extent of threeneighboring capacitor plate structures.

FIG. 14 is a top plan view of a linear mechanical control apparatusincluding a stationary first structure and a translatable secondstructure for a user interface with capacitive position and user touchdetection.

FIG. 15 is a partial sectional side elevation view taken along line15-15 of the control apparatus of FIG. 14.

FIG. 16 is a schematic diagram of an example sensing configuration ofconductive capacitor plate interconnections.

FIG. 17 is a table of an example position and user touch detectionsequence in the apparatus of FIG. 1.

FIG. 18 is a partial schematic diagram of an example capacitive senseinterface configuration with conductive capacitor plate interconnectionsfor position and user touch detection using a reduced number of generalpurpose I/O connections in the apparatus of FIG. 1.

FIG. 19 is a partial schematic diagram of an example capacitive senseinterface configuration with conductive capacitor plate interconnectionsfor position and user touch detection using a limited number of generalpurpose I/O connections in the linear apparatus of FIGS. 14 and 15.

DETAILED DESCRIPTION

In the drawings, like reference numerals refer to like apparatusthroughout, and the various features are not necessarily drawn to scale.In the following discussion and in the claims, the terms “including”,“includes”, “having”, “has”, “with”, or variants thereof are intended tobe inclusive in a manner similar to the term “comprising”, and thusshould be interpreted to mean “including, but not limited to . . . ”Also, the term “couple” or “couples” is intended to include indirect ordirect electrical or mechanical connection or combinations thereof. Forexample, if a first device couples to or is coupled with a seconddevice, that connection may be through a direct electrical connection,or through an indirect electrical connection via one or more interveningdevices and connections.

FIG. 1 shows a rotational mechanical control apparatus 100 for a userinterface. In one example, the apparatus 100 is a user interface controlknob that can be mechanically rotated by a user. The control apparatus100 can be used in any form of user interface or HMI, for example,industrial control panels, automobile dashboard controls, etc. Theexample of FIG. 1 provides a rotational control apparatus 100. Otherpossible examples include linear user interface control mechanisms, suchas slider controls as illustrated and described below in connection withFIGS. 14 and 15. FIG. 1 is a top view of a control knob user interfacecontrol apparatus 100 which can be used for a variety of applications,such as a volume knob for a vehicle audio system, and can include acapacitive touch sense on/off button in certain implementations. Theapparatus 100 includes conductive structures and pairs 102 of opticaldevices positioned on a fixed or stationary portion. A rotary portionincludes reflector structures 104 and 106. The rotary structure ismovable along a circumferential direction 108 relative to an axis 115 ofthe stationary portion. The optical device pairs 102 in one example areLEDs 111 and 112 positioned on the fixed or stationary portion, and oneor more conductive structures positioned on a rotating structure. Thecontrol apparatus 100 includes electrical connections 114, such as PCBtraces, to interface with the source and sensor optical devices 111 and112.

The apparatus in this example includes capacitive sensing circuitry thatdetects the relative position of the rotating structure to thestationary structure by sensing capacitances associated with theconductive structures on the fixed portion. In this example, moreover,the top face of the rotating structure can be touched by a user'sfinger, and the capacitive sensing circuitry can detect user touchevents as well as the position of the user's finger on the top face ofthe rotating structure. In certain examples, the apparatus 100 alsoincludes optical position sensing features and associated circuitry tocomplement the capacitive position sensing functions. Described examplesprovide improved capacitive sensing structures alone or in combinationwith mutual and self-capacitance measurements with a conductivestructure as field transducer to facilitate enhanced sensitivity fordetecting user touch events and/or control apparatus position.

The example control apparatus 100 includes a stationary first structure110 with a first (e.g., top or upper) side 113, facing out of the pagein FIG. 1. The first structure 110 includes 16 conductive capacitorplate structures 116 spaced from one another along a circumferentialfirst direction 108 on the first side 113. The conductive capacitorplate structures 116 are spaced from one another by a first distance 117(labeled D1) along the first direction 108. The first structure 110includes an integer number N=16 pairs 102 of LEDs 111, 112. In otherexamples, more or fewer than 16 conductive capacitor plate structures116 and LED pairs 102 can be used. In one example, the individual LEDpairs 102 include an optical source LED 111 and an optical sensor LED112. The LEDs 111 in this example have a first wavelength, and thesensor LEDs 112 have a different wavelength. The control apparatus 100includes electrical connections 118 to interface with the conductivecapacitor plate structures 116.

The control apparatus 100 includes a second structure 120 that ismovable relative to the first structure 110 along the first direction108. The second structure 120 includes an auxiliary conductive structure122 positioned on a second side 123 of the second structure 120 (e.g.,bottom side, facing into the page in FIG. 1). The auxiliary conductivestructure 122 moves with the second structure 120 along the firstdirection 108 to selectively modify a capacitance associated with agiven one of the conductive capacitor plate structures 116 when theauxiliary conductive structure 122 is positioned proximate the givencapacitor plate structure 116. The second structure 120 in this examplealso includes a transparent window or aperture 124 that allows lightfrom the optical sources 111 to pass through the second structure 120.

The control apparatus 100 includes an interface circuit 130 thatprovides excitation signals to the conductive capacitor plate structures116 and receives sense signals from the conductive capacitor platestructures 116 to measure capacitances of the apparatus 100. Theinterface circuit 130 performs a mutual capacitance test of groups ofthe conductive capacitor plate structures 116 and performs aself-capacitance test of individual ones of the conductive capacitorplate structures 116. The interface circuit 130 provides a positionsignal POSITION to a host system 131. The position signal represents aposition of the second structure 120 or a user's finger relative to aposition of the first structure 110 along the first direction 108according to signals from the conductive capacitor plate structures 116during one or both of the mutual capacitance test and theself-capacitance test. In one example, the interface circuit 130 alsodetermines the position signal POSITION at least partially according tosignals from the optical sensors 112, in addition to the signals fromthe capacitor plate structures 116.

In one example, the interface circuit 130 is provided on the PCB of thefirst user interface structure 110. The interface circuit 130 in FIG. 1includes a processor, such as a microcontroller unit (MCU) 132 with acommunications interface or output 133 that provides the positionsignals POSITION to the host circuit 131. The host circuit 131 in oneexample is a processor or user interface controller to operate a systemaccording to one or more control elements including the rotary knobcontrol apparatus 100. The processor 132 can be any suitable digitallogic circuit, programmable or pre-programmed, such as an ASIC,microprocessor, microcontroller, DSP, FPGA, etc., that operates toexecute program instructions stored in an internal or externalelectronic memory (not shown) to implement the features and functionsdescribed herein as well as other associated tasks to implement a userinterface control apparatus 100. In certain examples, the memoryconstitutes a non-transitory computer-readable storage medium thatstores computer-executable instructions that, when executed by theprocessor 132, perform the various features and functions detailedherein.

The illustrated interface circuit 130 also includes an optical (e.g.,LED) sense interface circuit 134 and a capacitive sense interfacecircuit 136. The processor 132 exchanges data and signaling with the LEDsense interface circuit 134 via a communications interface connection135. The sense interface circuit 134 is connected to the electricalconnections 114 to interface with the source and sensor optical devices111 and 112. The capacitive sense interface circuit 136 is connected tothe electrical connections 118 to interface with the conductivecapacitor plate structures 116. The processor 132 exchanges data andsignaling with the capacitive sense interface circuit 136 via acommunications interface connection 137. The processor 132 in oneexample executes program instructions to implement a mutual andself-capacitance test function or component 150.

FIG. 2 shows a top view of the stationary first structure 110 with thesecond structure 120 removed. The reflector structures 104, 106 and theauxiliary conductive structure 122 of the second structure 120 are shownin dashed line form for reference in FIG. 2. FIG. 2 schematicallyillustrates an example of the interconnection of the LEDs 111 and 112with the LED sense interface circuit 134. The interface circuit 134includes circuitry 202 for optical device biasing, signal multiplexingand switching, and general purpose input/output (GPIO) interfacingbetween the processor 132 and the LEDs 111, 112. In one example, thecircuit 134 includes biasing LED circuitry 202 to selectively forward orreverse bias selected ones of the LEDs 111 and/or 112. For example, thecircuit 134 forward biases one, some or all of the source LEDs 111 andreverse biases the sensor LEDs 112. The forward biasing causes theselected source LED(s) 111 to emit or transmit light of an associatedfirst wavelength λ1. Reverse biasing allows the selected sensor LED(s)112 to sense light of an associated second wavelength λ2 or less.

The wavelengths λ1 and λ2 can be the same or different. In theillustrated examples, the first wavelength λ1 is less than or equal tothe second wavelength λ2. In one example, the source LEDs 111 are whiteLEDs and the sensor LEDs 112 are red LEDs. The electrical connections114 allow the circuit 202 to selectively control the anode and cathodevoltages and signal conditions of each of the LEDs 111 and 112. Theprocessor 132 in certain implementations includes one or more analog todigital converters (ADCs or A/Ds, not shown), and the circuit 202includes switching circuitry and voltage supply and signal generators toselectively provide forward and reverse biasing of individual sourceLEDs 111 and interconnection of selected sensor LEDs 112 to GPIOterminals configured as ADC inputs. This allows the processor 132 toobtain digital values representing the sensor LED voltages to determinewhether a given sensor LED 112 is receiving a threshold amount of lightfrom the associated source LED 111 when the source LED 111 is forwardbiased. This, in turn, allows the processor 132 to determine whethereach given optical device pair 102 is proximate to the movable reflectorstructure(s) 104, 106, and hence to determine the position of the secondstructure 120 within the angular spacing resolution θLED of the opticaldevice pairs 102 (e.g., 22.5 degrees in the illustrated example).

In other examples, the LED interface circuitry 202 includes multiplexers(not shown) to allow sharing of a limited number of ADC inputs, and theoptical device pairs 102 can be actuated and measured individually or ingroups. The circuit 134 can include ADC circuits (with or without inputmultiplexing), and the ADC circuits provide converted values to theprocessor 132. In some examples, the processor 132 includes GPIOterminals that can be dynamically configured as digital outputs, digitalinputs, analog outputs, analog inputs and/or ADC inputs. In certainexamples, the circuit 202 selectively connects individual LED terminalsto a high voltage level, a low voltage level, and a DC input or providesa high impedance. The processor 132, in certain examples, controls theLED sense interface circuit 134 in multiphase operations to selectivelyforward bias one or more of the source LEDs 111 and to reverse biasselected ones of the sensor LEDs 112 to obtain sensor readings anddetermine the rotational position of the reflector structure orstructures 104, 106 relative to the first structure 110.

FIG. 3 shows a top view of the first structure 110 and schematicallyillustrates the capacitive rotational position and user touch eventdetection sense interface circuit 136. As seen in FIGS. 4-8 below, thefirst structure 110 in one example includes a transparent overlay formedabove the top side 113 of the first structure 110, not shown in FIG. 3.The circuit 136 includes capacitor excitation and sensing circuitry 302that selectively provides excitation voltage or current signals to thecapacitor plate structures 116 via the interconnections 118. The circuit302 also allows connection of ADC inputs (e.g., of internal ADC circuitsor GPIO/ADC inputs of the processor 132) to one or more of the platestructures 116 to sense capacitor voltage and/or current signals todetermine capacitance changes. The circuit 302 also allows connection ofone or more of the plate structures 116 to a controlled voltage to setthe voltage values of individual structures 116. The circuit 302 alsoallows floating of one or more of the plate structures 116, for example,by providing a high impedance (e.g., HI-Z) connection to selected onesof the structures 116.

The circuitry 136 in one example provides signals or converted valuesrepresenting voltage and/or currents of the capacitors formed by theplate structures 116 from which the processor 132 can detect thresholdamounts of capacitance variations caused by proximity of the conductivestructure 122 of the second structure 120 (FIG. 1) and/or a user'sfinger to a given one or group of the plate structures 116. From this,the processor 132 can determine the rotational position of theconductive structure 122 and/or the user's finger on the tope surface ofthe second structure 120, relative to the stationary first structure110.

In other examples, the auxiliary conductive structure 122 extends atleast partially over or near one or more conductive PCB traces or othercopper area connected in fixed manner to a reference voltage (e.g., GND)or to a GPIO, which can switch that copper to GND or supply level orother voltage level, or to a high impedance state, to enhance theresponse generated by the conductive structure 122. Example designsfacilitate distinguishing the presence of the structure 122 from theresponse of a user's finger touching the top surface of the structure120 in the wheel electrode area, as this touch event and respectivecapacitive response would not be influenced by this GND-VCC-inputswitching.

In the example control apparatus 100 of FIGS. 1-3, the interface circuit130 performs a series of mutual capacitance tests of individual groupsof the conductive capacitor plate structures 116 and one or moreself-capacitance tests of individual given ones of the conductivecapacitor plate structures 116. For these tests, the interface circuit130 provides an excitation signal to the given conductive capacitorplate structure 116 and receives a sense signal from that structure 116or from a neighboring conductive capacitor plate structure 116. Theinterface circuit 130 processes the received signals and determines(e.g., computes) mutual and self-capacitances (e.g., values thatrepresent a measured capacitance) according to (e.g., in response to orbased upon) the corresponding sense signal. The interface circuit 130processes the measured capacitances to identify the relative position ofthe first user interface structure 110 and the user's finger and/or therelative position of the first user interface structure 110 and thesecond user interface structure 120 according to the mutual capacitancesand one or more self-capacitances associated with the individualconductive capacitor plate structures 116.

Referring also to FIGS. 4-10, FIGS. 4 and 5 show partial sectional sideelevation views taken along line 4-4 in FIG. 1 to illustrate exampleelectric field lines during mutual capacitance measurements or tests inthe control apparatus 100. FIGS. 6-8 show partial sectional sideelevation views taken along line 4-4 in FIG. 1 to illustrate exampleelectric field lines during self-capacitance measurement for positionand/or user touch detection in the control apparatus 100 FIGS. 6 and 7show testing with a neighboring electrode grounded, and FIG. 8 showstesting with the neighboring electrode floating (e.g., HIZ or highimpedance state). FIG. 9 shows a mutual capacitance measurement circuitconfiguration example in the apparatus of FIG. 4 with no proximateauxiliary conductive structure 122 present. FIG. 10 shows the mutualcapacitance measurement circuit configuration example in the apparatusof FIG. 5 in the presence of the auxiliary conductive structure 122.

The conductive capacitor plate structures 116 are spaced from oneanother by a first distance 117 (labeled D1 in the drawings) along thefirst direction 108 (e.g., in the X direction for the illustratedportion of the apparatus 100 in FIGS. 4-8. The first structure 110includes a printed circuit board (PCB) 401 that includes the first side113 with the conductive capacitor plate structures 116, and a secondside 404 opposite to the first side 113. In addition, the firststructure 110 includes a transparent overlay structure 125. The PCB 401includes a further conductive structure 406 (e.g., a ground plane) onthe second side 404. The further conductive structure 406 is spaced fromthe conductive capacitor plate structures 116 by a second distance 402(labeled D2) along a second direction (e.g., the Z direction in FIGS.4-8). As shown in FIG. 5, the auxiliary conductive structure 122 isspaced from the conductive capacitor plate structures 116 by a thirddistance 403 (labeled D3) along the second direction. In this example,the first and second directions are perpendicular to one another,although not a requirement of all possible implementations. In theillustrated examples, the second distance 402 D2 is greater than thefirst distance 117 D1, and the first distance 117 D1 is greater than thethird distance 403 D3. This configuration enhances the sensitivity ofthe system to the relative positioning of the auxiliary conductivestructure 122 and the conductive capacitor plate structures 116. Therelative dimensions D1, D2 and D3 also improve the sensitivity fordetecting touch events by a user's finger (not shown) touching a topsurface 408 of the second structure 120. The distance D3 in oneimplementation is made as short as possible, and the gap distance D1between neighboring structures 116 is made at least equal the distanceD2 to GND, unless a driven shield (not shown) is provided between theTX/RX electrodes 116 and GND.

In certain implementations, the processor 132 performs a mutualcapacitance measurement as well as a single self-capacitance measurementwith respect to each given conductive capacitor plate structure 116. Inother implementations, the processor 132 performs a mutual capacitancemeasurement in addition to multiple self-capacitance measurements withrespect to each conductive capacitor plate structure 116. The processor132 in one example performs the measurement sequence periodically inorder to continuously monitor the control apparatus 100 with respect tothe position of the second structure 120 relative to the first structure110, in addition to monitoring for detected user touch events. In eachsequence, in one example, the processor 132 implements multiple mutualcapacitance measurements (e.g., with respect to each of the example 16given structures 116), and two sets of multiple self-capacitancemeasurements (e.g., with respect to each of the example 16 givenstructures 116), and obtains multiple sets of measured capacitances. Inthe illustrated example, the processor 132 compares the measuredcapacitance values of each measurement set, and determines the positionof the rotatable second structure 120 based on the maximal (e.g.,highest) measured capacitances and the corresponding locations of themaximal measurements. In addition, the processor 132 in one exampledistinguishes between identified second structure position and usertouch events based on the measured capacitance values.

FIGS. 4, 5, 9 and 10 illustrate example mutual capacitance testing withrespect to a given conductive capacitor plate structure 116. During themutual capacitance testing, the interface circuit 130 provides anexcitation signal to the given conductive capacitor plate structure 116(e.g., the transmit or TX electrode) and receives a sense signal fromone or more neighboring conductive capacitor plate structures 116 (e.g.,the receive or RX electrode). FIGS. 4 and 5 show this test configurationand corresponding field lines (arrows in the drawings) for testing themutual capacitance of a given structure 116 on the left, and aneighboring structure 116 on the right. It will be appreciated that thegiven structure 116 can have a similarly connected neighbor to the left(not shown in FIGS. 4-8). FIG. 4 shows the situation in which therotatable auxiliary conductive structure 122 is not near the given orneighboring structures 116. FIG. 5 shows the situation in which therotatable auxiliary conductive structure 122 at least partially overliesthe given conductive capacitor plate structure 116 and the neighboringstructure 116.

FIG. 9 shows a schematic circuit representation 900 of the situation inFIG. 4 when the auxiliary conductive structure 122 is not proximate thegiven and neighboring electrode structures 116. The diagram 900 in FIG.9 illustrates a first capacitance 901 (labeled C_(TX-GND)) thatrepresents the capacitance between the given (e.g., TX) conductivecapacitor plate structure 116 and the ground plane conductive structure406. The diagram 900 also shows a second capacitance 902 (labeledC_(TX-Rx)) that represents the capacitance between the given andneighboring structures 116, as well as a third capacitance 903 (labeledC_(RX-GND)) that represents the capacitance between the neighboring(e.g., RX) conductive capacitor plate structure 116 and the ground planestructure 406. In this case the auxiliary structure 122 is not present,thus the electric field E_(TX-RX), which is primarily responsible forthe sensed signal at the RX electrode, is mainly defined by the gapbetween TX and RX electrodes 116.

FIG. 10 shows a schematic circuit representation 1000 of the situationin FIG. 5 in the presence of the auxiliary conductive structure 122. Inthis case, the capacitances 901, 902 and 903 are present in the circuit.In addition, the circuit includes a capacitance 1001 (labeledC_(TX-AUX)) that represents the capacitance between the given (e.g., TX)conductive capacitor plate structure 116 and the proximate auxiliaryconductive structure 122, as well as a capacitance 1002 (labeledC_(AUX-RX)) that represents the capacitance between the auxiliaryconductive structure 122 and the neighboring (e.g., RX) conductivecapacitor plate structure 116. In this case the auxiliary conductivestructure 122 is present, which reduces the electric field E_(TX-RX),but adds an ETX-RX component that includes of the serial E-fieldsE_(TX-AUX) E_(AUX-RX) which are now all together responsible for thesensed signal at the RX electrode 116. Due to the larger capacitanceC_(TX-RX), the sensed signal at the RX electrode 116 will besignificantly higher than in FIGS. 4 and 9, and the processor 132 candetect the presence of the auxiliary conductive structure 122.

The electrode configuration of TX and RX electrodes is controlled byprogram instructions executed by the processor 132, and theconfiguration of the electrodes can be changed from TX to RX and viceversa. In addition, the electrodes 116 are not only a combination ofTX/RX pairs, but the TX/RX can commute around the wheel structure, andthe TX electrode at the same time can be TX for two neighboredelectrodes 116, configured as RX electrodes, one in the clockwise, andthe other in the counter clockwise direction. In this manner, theprocessor 132 performs a differential measurement in certain examples,as the auxiliary structure 122 can be designed to cover the area of twoneighbored electrodes 116.

In one example, the MCU processor 132 implements the mutual andself-capacitance test component 150 and the capacitor sensor interfacecircuit 136 connects the given structure 116 (e.g., TX) to an analogoutput general-purpose I/O (GPIO) of the processor 132 in order toprovide a transmit (TX) signal to the given conductive capacitor platestructure 116. The processor 132 and the interface circuit 136 connectsthe neighboring structure 116 (e.g., the RX electrode) to an analog todigital converter (ADC) function of a different GPIO of the processor132 in order to measure a received signal from the neighboringconductive capacitor plate structure 116. Any suitable AC, DC or rampingexcitation (e.g., TX) signal can be applied to the given conductivecapacitor plate structure 116 operating as a TX electrode. In oneexample, the processor 132 applies a series of excitation signals to theTX electrode 116 by operating a connected GPIO that acts as an analogoutput signal source. In one example, the excitation signal patternsinclude a first signal that ramps up from a ground level or otherpredefined level to charge the capacitances to a constant predeterminedDC level.

Once the capacitances are set to a known starting state, the processor132 switches the TX GPIO to a function that supports transfer of theexisting charge to apply or create charge on the RX electrode 116 by theTX-RX capacitance. After one charge cycle, the processor switches to atransfer mode that transfers the created charge of the RX electrode 116to an internal reference or sample capacitor of the MCU 132 or of themeasuring (e.g., RX) GPIO, or to a reference capacitance of thecapacitor sensor interface circuitry 136. In one example, a chargetransfer circuit transfers the created RX electrode charge to thereference capacitor. The processor measures the number of internal clockcycles to charge the internal capacitance to a known value. Because theinternal capacitance value is known, the processor 132 determines themeasured capacitance (e.g., mutual or self-capacitance) according to(e.g., in response to or based upon) the number of required chargecycles to reach a certain threshold voltage on the referencecapacitance. In this example, the processor 132 effectively measures thecharge transfer to determine the measured capacitance. In otherexamples, the processor 132 uses a fixed charge time and measures theresulting electrode voltage to determine the measured capacitance. Inother examples, the processor 132 uses a single charge or dischargeslope to perform capacitance measurement. In one example, the processor132 uses a voltage threshold and measures the time. In some examples,the processor 132 implements multiple charge and discharge cycles (e.g.,oscillations) during a fixed gate time, and measures the number ofcharge discharge/oscillation cycles to determine the capacitance. Inthese examples, the processor 132 provides the excitation signal to thegiven conductive capacitor plate structure 116 and receives the sensesignal from a neighboring conductive capacitor plate structure 116 toperform the mutual capacitance test of the individual groups of theconductive capacitor plate structures 116. In certain examples,moreover, the processor 132 uses two adjacent neighboring conductivecapacitor plate structures 116 in performing capacitance testing of agiven conductive capacitor plate structure 116 for the mutualcapacitance measurements.

FIGS. 6 and 7 illustrate a first one of two different exampleself-capacitance measurements in the control apparatus 100. FIG. 6 showsa first self-capacitance measurement configuration and associated fieldlines with the given conductive capacitor plate structure 116 connectedto receive an excitation signal from a corresponding GPIO of theprocessor 132. The given structure 116 operates as both a TX electrodeand an RX electrode for the self-capacitance measurements. In theexample of FIG. 6, the processor 132 grounds the neighboring structure116 (e.g., the same potential as the ground plane structure 406) using aconnected GPIO. FIG. 7 shows the first self-capacitance measurementconfiguration and corresponding electric field lines in the presence ofthe auxiliary conductive structure 122, which changes the field linesand the corresponding measured self-capacitance associated with thegiven conductive capacitor plate structure 116. In one example, theprocessor 132 performs the first self-capacitance test for theindividual conductive capacitor plate structures 116 by providing theexcitation signal to the given conductive capacitor plate structure 116,setting the voltage of the neighboring conductive capacitor platestructure 116 to a first voltage value (e.g., ground as in FIGS. 6 and7) while providing the excitation signal to the given conductivecapacitor plate structure 116. The processor 132 receives the sensesignal from the given conductive capacitor plate structure 116, anddetermines a first self-capacitance associated with the given conductivecapacitor plate structure 116 according to the corresponding sensesignal.

FIG. 8 shows a second self-capacitance measurement in the controlapparatus 100. In this example, the processor 132 performs the secondself-capacitance test for the individual conductive capacitor platestructures 116 by providing the excitation signal to the givenconductive capacitor plate structure 116 and setting the voltage of theneighboring conductive capacitor plate structure 116 to a second voltagevalue or allowing the neighboring conductive capacitor plate structure116 to float while providing the excitation signal to the givenconductive capacitor plate structure 116. The processor 132 receives thesense signal from the given conductive capacitor plate structure 116,and determines a second self-capacitance associated with the givenconductive capacitor plate structure 116 according to the correspondingsense signal. In this example, the processor 132 processes the measuredcapacitances to identify the relative position of the first userinterface structure 110 and the user's finger or the second userinterface structure 120 according to the mutual capacitances and firstand second self-capacitances associated with the individual conductivecapacitor plate structures 116.

The processor 132 in one example can distinctly identify the presence orabsence of the auxiliary conductive structure 122 and/or the presence orabsence of a user's finger at a given location along the direction 140based on measured capacitance values obtained in each measurement cycleaccording to (e.g., in response to or based upon). In one example, theprocessor 132 performs a mutual capacitance measurement as well as firstand second self-capacitance measurements for each of the 16 givenelectrodes (e.g., capacitor plate structures) 116 in each measurementcycle, and computes 16 sets of three capacitance measurements.

In another example, the processor 132 performs the capacitancemeasurements with respect to the first and second neighboring electrodesfor each given electrode 116, and computes 16 sets of five capacitancemeasurements (e.g., a mutual capacitance measurement, a firstself-capacitance measurement relative to the first neighboringelectrode, a first self-capacitance measurement relative to the secondneighboring electrode, a second self-capacitance measurement relative tothe second neighboring electrode, and a second self-capacitancemeasurement relative to the second neighboring electrode). In oneexample, the processor 132 differentiates according to the differencebetween the first and second measured self-capacitance values for theindividual given electrodes 116, referred to hereinafter as aself-capacitance difference value. In the described examples illustratedin FIGS. 4-8, the self-capacitance difference value is greatest withrespect to a given electrode 116 for the case where the auxiliaryconductive structure 122 and a user's finger are proximate the givenelectrode 116. This condition corresponds to the highest electric fieldstrength associated with the corresponding neighboring electrode 116. Alower self-capacitance difference value corresponds to the case wherethe auxiliary conductive structure 122 is present, and no user finger ispresent at or near the given electrode 116. A still lowerself-capacitance difference value occurs when the user's finger ispresent, and the auxiliary conductive structure 122 is absent, and thelowest self-capacitance difference value corresponds to the case whereno user's finger is present and the auxiliary conductive structure 122is absent. The processor 132 in one example compares the measuredcapacitance values to determine the relative levels for the first andsecond self-capacitance values to distinguish these four conditions, andselectively identifies the position of the movable auxiliary conductivestructure 122 and/or the presence and position of a user's finger in thecontrol apparatus 100. In addition, the processor 132 in certainexamples differentiates between potential positioned identificationsbased on the presence of multiple auxiliary conductive structures 116,for example, as shown in FIGS. 11-13.

FIGS. 11-13 illustrate different example conductive capacitor platestructure shapes and auxiliary conductive structure shapes which can beused. In addition, different numbers of auxiliary and capacitivestructures can be used in different implementations. FIG. 11 shows anexample including two movable auxiliary conductive structures 122 withangular circumferential lengths approximately covering radially outerportions of two neighboring capacitor plate structures 116 The auxiliaryconductive structures 122 in this example are positioned on radiallyopposite sides of the axis 115, although not a strict requirement of allpossible implementations. FIG. 12 shows another non-limiting example ofthe 16 conductive capacitor plate structures 116 and two example movableauxiliary conductive structures 122. In this example, the auxiliarystructures 122 have angular circumferential lengths approximatelycovering radially outer portions of three neighboring capacitor platestructures 116. FIG. 13 shows yet another example with 16 conductivecapacitor plate structures 116 and two example movable auxiliaryconductive structures 122 that approximately cover the circumferentialand radial extent of three neighboring capacitor plate structures 116.The radial extent of the auxiliary conductive structures 122 in oneexample covers a significant radial spacing of the conductive capacitorplate structures 116, and can even cover them radially completely asshown in FIG. 13. A larger covered area results in a higher robustnessof the capacitive-mechanical rotation detection due to a higherresponse.

FIGS. 14 and 15 illustrate another possible implementation 100, in whichthe first direction 108 is linear. In this case, 17 structures 116 arelinearly spaced from one another (labeled P1, P2, P3, P4, P5, P6, P7,P8, P9, P10, P11, P12, P13, P14, P15, P16, and a duplicate P1). FIG. 14shows a top view and FIG. 15 shows a side view. The linear mechanicalcontrol apparatus 100 includes a stationary first structure 110 and alinearly translatable second user interface structure 120 for a userinterface or HMI. The control apparatus 100 operates in generallysimilar fashion to the rotational apparatus 100 discussed above, withthe second structure 120 translatable along a linear first direction 108(along the X direction in FIGS. 14 and 15) relative to the stationaryfirst structure 110. Like the apparatus 100 discussed above, the controlapparatus 100 of FIGS. 14 and 15 can include both capacitive and opticallinear position detection features, where the LEDs and reflectors areomitted in the illustrated example. The first structure 110 in FIG. 15also includes a transparent protective overlay 125 with a bottom sidethat extends over the top surfaces of the conductive capacitorstructures 116. The conductive capacitor plate structures 116 on thefirst side 113 form an integer number capacitors. The second structure120 includes a bottom or second side 123 with a conductive structure 122that faces the conductive capacitor plate structures 116 of the firststructure 110. Depending on the position of the second structure 120,the conductive structure 122 selectively modifies the capacitance of agiven one of the capacitor plate structures 116 when the conductivestructure 122 is positioned proximate the given structure 116.

Referring now to FIGS. 16-19, in one example, the processor 132 usesmatrix testing techniques to perform mutual and self-capacitance testingor measurements in the control apparatus 100. FIG. 16 shows an examplesensing configuration 1600 including conductive capacitor plateinterconnections. In this example, CAPx.y designates a multiplexerinterconnection in an interface circuit 136 or in internal multiplexersof the MCU processor 132, using an integer number “x” multiplexers, eachhaving “y” inputs. The individual multiplexers in certain examples areassociated with a corresponding general-purpose I/O (GPIO).

FIGS. 18 and 19 illustrate detailed examples for rotary and linearcontrol apparatus examples 100, respectively, where “x” ranges from 0-3and “y” ranges from 0-3. FIG. 17 shows a table 1700 that illustrates anexample position and user touch detection truth table used in oneexample of the control apparatus 100, including 16 capacitor testsCT1-1, CT1-2, CT1-3, CT1-4, CT1-5, CT1-6, CT1-7, CT1-8, CT1-9, CT1-10,CT1-11, CT1-12, CT1-13, CT1-14, CT1-15 and CT1-16 indicated in a firstcolumn of the table 1700. The second column of the table showsinterconnections for that particular test. For example, for detection ofa touch event at position CT1-1 (P1), a capacitive response is expectedin this example at a connection CAP1.3, a connection CAP0.0 and aconnection CAP2.0. In one example, where the auxiliary conductivestructure 122 and/or a user's finger is present, the maximum response isexpected for this condition at the connection CAP0.0, and the signalingfrom the neighboring connections CAP1.3 and CAP2.0 exhibit lower butnoticeable responses. For this particular test, the conductive capacitorplate structure 116 associated with CAP0.0 is the center or given (e.g.,TX) electrode, and is tested along with its neighboring electrodesCAP1.3 and CAP2.0. In operation, the processor 132 sequentially performsthe 16 tests for each of the mutual capacitance tests, and the first andsecond self-capacitance tests. FIG. 18 shows a configuration 1800 andincludes the corresponding electrical connections 118 for the rotaryimplementation, in which the conductive capacitor plate structures 116are sequentially labeled P1-P16 in a clockwise manner. In the first testCT1-1 in the table 1700 of FIG. 17, for example, the conductivecapacitor plate structure 116 associated with CAP0.0 is labeled P1 inFIGS. 18 and 19. When this plate structure 116 is the given structurebeing tested, the structure 116 labeled P1 is the center or given (e.g.,TX) electrode, and is tested along with its counterclockwise neighborP16 (CAP1.3) and its clockwise neighbor P2 (CAP2.0). FIG. 19 illustratesa corresponding linear configuration interconnection example 1900. Inorder to facilitate the testing interconnection and operation for agiven electrode and neighboring electrodes, the linear example 100includes duplicate P1 electrodes 116 at opposite ends of the linearconfiguration.

Modifications are possible in the described embodiments, and otherembodiments are possible, within the scope of the claims.

What is claimed is:
 1. An apparatus comprising: a first structure,comprising capacitor plate structures on a first side of the firststructure, wherein the capacitor plate structures are spaced along afirst direction on the first side; a second structure movable relativeto the first structure along the first direction, the second structurehaving a second side facing the first side of the first structure; anauxiliary conductive structure disposed on the second side of the secondstructure, wherein the auxiliary conductive structure is configured tomove with the second structure in the first direction to selectivelymodify a capacitance associated with a first capacitor plate structureof the capacitor plate structures upon the auxiliary conductivestructure being positioned proximate the first capacitor platestructures; and an interface circuit configured to: provide anexcitation signal to the capacitor plate structures; and receive a sensesignal from the capacitor plate structures.
 2. The apparatus of claim 1,wherein the interface circuit is further cinfigured to perform a mutualcapacitance test of groups of the capacitor plate structures and toperform a self-capacitance test of individual ones of the capacitorplate structures, to provide a position signal according to signals fromthe capacitor plate structures during one of the mutual capacitance testor the self-capacitance test.
 3. The apparatus of claim 2, wherein: thecapacitor plate structures are spaced from one another by a firstdistance along the first direction; the first structure furthercomprises: a second side opposite to the first side; and a furtherconductive structure on the second side, the further conductivestructure being spaced from the capacitor plate structures by a seconddistance along a second direction; and the auxiliary conductivestructure is spaced from the capacitor plate structures by a thirddistance along the second direction.
 4. The apparatus of claim 3,wherein: the second distance is greater than the first distance; and thefirst distance is greater than the third distance.
 5. The apparatus ofclaim 4, wherein the interface circuit is configured to provide theexcitation signal to the first capacitor plate structure and to receivethe sense signal from a neighboring capacitor plate structure to performthe mutual capacitance test of the groups of the capacitor platestructures.
 6. The apparatus of claim 5, wherein the interface circuitis configured to provide the excitation signal to the first capacitorplate structure, receive the sense signal from the first capacitor platestructure, and control a voltage of the neighboring capacitor platestructure to perform the self-capacitance test of the first capacitorplate structure.
 7. The apparatus of claim 6, wherein: the interfacecircuit is configured to provide the excitation signal to the firstcapacitor plate structure, receive the sense signal from the firstcapacitor plate structure, and set the voltage of the neighboringcapacitor plate structure to a first voltage value to perform a firstself-capacitance test of the first capacitor plate structure; and theinterface circuit is configured to provide the excitation signal to thefirst capacitor plate structure, receive the sense signal from the firstcapacitor plate structure, and allow the neighboring capacitor platestructure to float to perform a second self-capacitance test of thefirst capacitor plate structure.
 8. The apparatus of claim 6, wherein:the interface circuit is configured to provide the excitation signal tothe first capacitor plate structure, receive the sense signal from thefirst capacitor plate structure, and set the voltage of the neighboringcapacitor plate structure to a first voltage value to perform a firstself-capacitance test of the first capacitor plate structure; and theinterface circuit is configured to provide the excitation signal to thefirst capacitor plate structure, receive the sense signal from the firstcapacitor plate structure, and set the voltage of the neighboringcapacitor plate structure to a second voltage value to perform a secondself-capacitance test of the first capacitor plate structure.
 9. Theapparatus of claim 2, wherein the interface circuit is configured toprovide the excitation signal to the first capacitor plate structure andto receive the sense signal from a neighboring capacitor plate structureto perform the mutual capacitance test of the groups of the capacitorplate structures.
 10. The apparatus of claim 2, wherein the interfacecircuit is configured to provide the excitation signal to the firstcapacitor plate structure, receive the sense signal from the firstcapacitor plate structure, and control a voltage of a neighboringcapacitor plate structure to perform the self-capacitance test of thefirst capacitor plate structure.
 11. The apparatus of claim 10, wherein:the interface circuit is configured to provide the excitation signal tothe first capacitor plate structure, receive the sense signal from thefirst capacitor plate structure, and set the voltage of the neighboringcapacitor plate structure to a first voltage value to perform a firstself-capacitance test of the first capacitor plate structure; and theinterface circuit is configured to provide the excitation signal to thefirst capacitor plate structure, receive the sense signal from the firstcapacitor plate structure, and allow the neighboring capacitor platestructure to float to perform a second self-capacitance test of thefirst capacitor plate structure.
 12. The apparatus of claim 10, wherein:the interface circuit is configured to provide the excitation signal tothe first capacitor plate structure, receive the sense signal from thefirst capacitor plate structure, and set the voltage of the neighboringcapacitor plate structure to a first voltage value to perform a firstself-capacitance test of the first capacitor plate structure; and theinterface circuit is configured to provide the excitation signal to thefirst capacitor plate structure, receive the sense signal from the firstcapacitor plate structure, and set the voltage of the neighboringcapacitor plate structure to a second voltage value to perform a secondself-capacitance test of the first capacitor plate structure.
 13. Theapparatus of claim 2, further comprising: optical sources disposed onthe first side of the first structure, the optical sources configured toselectively direct light away from the first side; optical sensorsdisposed on the first side of the first structure, the optical sensorsconfigured to selectively sense light directed toward the first side ofthe first structure, the optical sensors positioned proximatecorresponding optical sources, the optical sources and optical sensorsforming optical device pairs spaced from one another along the firstdirection; and a reflector disposed on the second side of the secondstructure, the reflector configured to move along the first direction toselectively reflect light from one of the optical sources to thecorresponding optical sensor; and wherein the interface circuit isfurther configured to provide the position signal according to signalsfrom the optical sensors and signals from the capacitor platestructures.
 14. The apparatus of claim 1, wherein the first direction iscircumferential relative to an axis.
 15. The apparatus of claim 1,wherein the first direction is linear.
 16. A method comprising:performing a mutual capacitance test, comprising: providing a firstexcitation signal, by an interface circuit, to a first capacitor platestructure of capacitor plate structures, wherein the capacitor platestructures are spaced along a first direction on a stationary firststructure; receiving a first sense signal, by the interface circuit,from a second capacitor plate structure of the capacitor platestructures; and determining, by the interface circuit, a mutualcapacitance associated with the first capacitor plate structure and thesecond capacitor plate structure, according to the first sense signal;performing a self-capacitance test, comprising: controlling, by theinterface circuit, a voltage of the second capacitor plate structure,while providing a second excitation signal to the first capacitor platestructure; receiving a second sense signal, by the interface circuit,from the first capacitor plate structure; and determining, by theinterface circuit, a self-capacitance associated with the firstcapacitor plate structure according to the second sense signal; andprocessing the mutual capacitance and the self-capacitance to identify arelative position of the stationary first structure and a secondstructure, the second structure movable in the first direction.
 17. Themethod of claim 16, further comprising processing the mutual capacitanceand the self-capacitance to identify a relative position of thestationary first structure and a finger.